Want to improve highway mileage

[krousdb]

http://www.gassavers.org/forum_topic/gassavers_dictionary_of_technical_terminology.html

[GasSavers_Ryland]

I tend to drive 75mph, but the last few weeks I've taken a rout that requires me to stay around 60-65mph, going 75mph I'll get 39.5-40mpg going 65mph I'll top out around 44mpg, it's already close to a 3 hour drive every monday morning, so droping my speed by 10mph adds half an hour to my commute, or half an hour that I'm not sleeping or getting paid.

I changed the underhood fuel filter a year ago when I got the car... is there another filter? I should find out, at the same time I checked fuel presure, and it was within spec.
my air filter is a washable foam "turboflow" or something like that foam air filter, I've washed it twice, re-oiled it with foam filter oil, I've also put in a standerd paper filter for a tank or two of gas to make sure that wasn't draging me down.
when I replaced my throttle body a few months back (had a dead spot in the TPS) I sprayed some carb cleaner in the intake manifold, and also peeked in the injector holes in the intake manifold when I had the injectors out, to clean the injectors I removed them, scrubed off the carbon build up, soaked them in Sea Foam, and brushed them with a tooth brush untill they looked clean, I did not take them appart, and their internal resistance is within spec.
I have a 49 state civic vx, with a brand new 5 wire NGK sensor, o2 sensor wires are in good shape with a clean plug.
I had an alinement done a year ago and it still goes straight down the road, I plan to get an alinement done again after I replace some of the suspention bushings.
I'll look in to cleaning the intake manifold more.
I checked my valve clearnces today, last did it 15,000 miles ago, they were pretty good, 3 exaust valves were maybe .001" tight, one intake was just a little loose, they are now all exact, so we'll see if that helps any, but I think they were all close enough that it shouldn't matter.
I'm really hoping to get my highway mileage up, as this june we are planing to do a road trip out west, 3 people, 2000+ round trip, and every extra will help.

[JanGeo]

You need to reduce friction - add some oil additives. I don't go 75 in my xB but my 280 mile trip yesterday at night in rain got me 40.1 mpg there and 41.3 back doing 60-65 and try to get behind a bigger vehicle or a line of vehicles - if the line of vehicles is big enough they get the air moving your way and it greatly reduced drag. I was going 65mph and getting 55 mpg for a while behind a tractor trailer truck.

[krousdb]

Originally Posted by Ryland

I tend to drive 75mph, but the last few weeks I've taken a rout that requires me to stay around 60-65mph, going 75mph I'll get 39.5-40mpg going 65mph I'll top out around 44mpg, it's already close to a 3 hour drive every monday morning, so droping my speed by 10mph adds half an hour to my commute, or half an hour that I'm not sleeping or getting paid.

In the Prius on a warm day, 65 MPH = 55 MPG and 55 MPH = 65 MPG. I would rather go to bed 1/2 hour early and leave for work 1/2 hour early for one day a week than to give away 10 MPG. But thats just me. I am a nut!

[n0rt0npr0]

Ryland,

Brake Drag could be a factor. Just do a search on the site for more info into that.

Otherwise the aero mods are worth some research.

[rh77]

For me, driving at 60 mph or under worked wonders for the highway MPG. I know it sucks getting passed by everyone, but I get 40+ on the highway at 57 mph and about 20-30 MPG at 80 mph -- it's just the simple physics of wind resistance vs. power. I just need to get the city driving figured out because that's really killing my mileage right now.

RH77

[Compaq888]

Originally Posted by n0rt0npr0

Otherwise the aero mods are worth some research.

BINGO!!!!!!!!!!!!!!!!!!!!!!!!!!

we have a winner. It doesn't matter how fast you're going on the freeway, aero stuff that's done right always helps.

[n0rt0npr0]

Originally Posted by rh77

For me, driving at 60 mph or under worked wonders for the highway MPG. I know it sucks getting passed by everyone, but I get 40+ on the highway at 57 mph and about 20-30 MPG at 80 mph -- it's just the simple physics of wind resistance vs. power. I just need to get the city driving figured out because that's really killing my mileage right now.

RH77

Some sweet info...
You could potentially log all speeds and create your own specific non-linear graph. Lucky OBDII people!